Ankara sees the YPG as an extension of the outlawed Kurdistan Workers Party, which has waged a three-decade insurgency in Turkey's mainly Kurdish southeast.
Erdogan said he warned Trump that Turkey would combat YPG if the group posed any security threat. The department says the ambassador met Wednesday with Tom Shannon, the acting deputy secretary of state and highest-ranking career USA diplomat.
Citing a cross-border offensive Turkey launched against IS and the YPG in Syria previous year, Erdogan said "we won't hesitate to launch similar operations if we see the need".
"The Turkish government owes an apology; perhaps they forgot we have unalienable rights in this country", Cardin tweeted.
Ankara launched its "Euphrates Shield" operation inside Syria a year ago, backing Syrian rebels with tanks, air strikes and special forces to sweep Islamic State from its southern border - and stop the advance of the YPG. "We are telling you this now in advance", Erdogan said.
Turkish Foreign Minister Mevlut Cavusoglu said on Thursday he wanted Brett McGurk, the U.S. special envoy to the coalition against Islamic State, removed from his post, saying he supported Kurdish militants. "Because we have no time to lose", he said. But he said Mr McGurk was openly supporting the Kurds and "it would be beneficial" if the U.S. special envoy left.
Differences over Syria policy have caused friction with Washington, a North Atlantic Treaty Organisation ally of Turkey's. By facilitating Armenian Genocide denial, by remaining silent regarding Turkey's illegal blockade of Armenia, by disregarding its support for ISIS and al Qaida, by overlooking Turkey's suppression of its religious and national minorities and its widening repression against its citizens-at-large, the US has only emboldened the Erdogan regime to become more aggressive, both inside and outside of Turkey.
Last month, Turkish warplanes bombed Kurdish fighters in Iraq's Sinjar region and YPG militia in Syria. Video shows people pushing past police to confront a small group of protesters across the street in Sheridan Circle.
"We should throw their ambassador the hell out of the United States of America ..."
The State Department has criticized the Turkish government over violence outside its embassy, where Erdogan's security staff broke up an anti-government protest.
Sen. John McCain of Arizona, the chairman of the Armed Services Committee, expressed outrage Thursday at video that appears to show Erdogan's bodyguards violently breaking up a protest earlier this week outside the Turkish ambassador's residence in Washington.